As a rule, agricultural vehicles or other working vehicles comprise elements that can be adjusted, i.e., moved linearly or swiveled, with respect to the working vehicle by associated actuators. Such elements include, for a tractor, an implement placed on a front or rear power lift of a tractor, for soil cultivation, for sowing, or for spreading fertilizers or other chemicals for example; for a self-propelled field sprayer, a height-adjustable sprayer boom and/or one that can swivel about an axis extending in the forward direction; for a combine harvester or a forage harvester, a harvesting attachment which, for height adjustment, can swivel around a horizontal axis, transversely oriented toward the forward direction (as a rule, the rotational axis of an upper inclined conveyor roller or cutter head) and/or for parallel orientation on a slope, about an axis that extends in the forward direction, or for height adjustment of its discharge end, a spout of a forage harvester that can be adjusted in height about a horizontal axis and/or can be adjusted in height about the vertical axis. The target position of the actuator and thus the adjustable element is specified by an operator via a suitable interface or by an automatic control device, working together with sensors.
Since, as a rule, the working vehicle is supported by air-filled (and thus elastically flexible) tires on the ground and/or can be provided with a suspension between the wheels or track roller units and the body of the working vehicle, the system consisting of the adjustable element and the working vehicle is excited to a pitching oscillation (pitch) with every adjustment of the actuator; this can have a disturbing effect during operation. Thus, cutting mechanisms can have a width of 12 m or more, and if they are guided in heights of a few cm over the ground, a desired cutting height can occasionally not be maintained due to the vibration arising from a height adjustment. Furthermore, the working vehicle is excited to pitching oscillations as a result of the flexible tires and/or the suspension, if the working vehicle changes its travelling speed, automatically or via an operator input, or if it travels over bumps. Rolling oscillations in a lateral direction are also possible, if, for example, wheels on only one side travel over bumps.
For damping such pitching oscillations on a tractor with a hinged plow, the proposal was made that during road travel, the raised plow be actively damped by detecting force changes caused by pitching oscillations, using sensors for the load of the front axle, the traction, or the pressure in a hydraulic cylinder (DE 34 46 811 A1). The pitching oscillation of the system consisting of a plow and tractor is accordingly damped by a suitable height adjustment of the plow, which counteracts the vibration. In a similar manner, a proposal is made in DE 10 2010 017 459 A1 that any vibrations of a spout of a forage harvester be detected with a sensor for detecting the position of the spout relative the forage harvester, or the pressure in the hydraulic cylinder used for height adjustment of the spout, in order to detect pitching oscillations of the forage harvester and to control the hydraulic cylinder contrary to the vibration if necessary.
Furthermore, in the prior art, there are known control circuits that are equipped with a sensor for detecting the respective position of the adjustable element; their signal is used to feed back the actual position of the element to a control circuit (see, for example US 2009/0277145 A1 for a height adjustment of a harvesting attachment of a combine harvester). In this way, any deviations of the element from its target position, caused, among other things, by the pitching oscillation of the working vehicle, are detected and fed back to the control circuit in order to keep the harvesting attachment in its desired height above the ground, but any pitching oscillations of the system consisting of the harvesting machine and the harvesting attachment are not systematically damped.
Accordingly it is known from the prior art, especially from DE 34 46 811 A1, that any pitching oscillations of a system consisting of a working vehicle and an element that can undergo a height adjustment relative to the vehicle can be damped by means of a suitable height adjustment of the adjustable element. Such a procedure, however, encounters limits when the position of the element is to remain with a defined range during operation, for example, if the height-adjustable element is a harvesting attachment that is not to penetrate into the soil or cut above the ears, or if a specific plow depth is to be maintained.